Originally Posted by RobOnLI

Anything but "Y" fares. DL continues to offer immediate upgrades on "Y" fares for any elite (provided there is V/X availability on the flight). If there is not then "Y" fares go to the battlefield upgrade process and have priority over all other elites on any other fare class including B, M, H, Q, K, L, U T. With "Y" fares the second factor for upgrade is time of request rather than status. So a Silver on a "Y" fare who requests their upgrade before a Plat on a "Y" fare will receive the upgrade first.

-RM